This invention relates to an apparatus for assembling and disassembling the threadably engageable members of a device having two or more such members. In particular, the invention is concerned with an apparatus for the assembly and disassembly of interchangeable members of a surgical acoustic device.
Ultrasonic surgical devices for performing a number of surgical procedures are known in the art. A representative device is a hand-held instrument comprising a surgical handpiece incorporating a resonant vibrator having an electrically operated transducer which produces ultrasonic vibrations which are amplified and transmitted to a tool tip for the fragmentation of biological tissue. Typical examples of such a device are disclosed in U.S. Pat. Nos. 4,223,676 and 4,425,115.
The structure of an ultrasonic surgical device such as that disclosed in the aforementioned patents depends not only upon the technical and functional requirements of a resonant vibrator but also upon its surgical application. Thus, developments have been made over the years to determine the length and diameter of the tool required for a useful surgical device in various operative sites. Extensive experience has determined that an especially useful assembly can be made from a combination of members that are threaded together for easy interchange. The joint between the tool member and the adjacent member of the resonant vibrator is desirably made at a point which will provide maximum amplification at the tool tip. However, this is generally the point of greatest stress and requires a strong coupling to maintain the members in appropriate contact and avoid mechanical losses and damage during ultrasonic vibrations.
In practice, it is important that intimate contact be maintained between the threadably engaged members during operation of the device to maximize energy transfer, minimize mechanical losses and obtain consistent performance during surgical use. In particular, it is important to minimize parasitic vibrations during operation which may cause failure of either or both of the coupled acoustic members.
Experience with surgical devices also has determined an appropriate coupling force or torque for certain assemblies. The torque should be such that the acoustic members can not be adequately assembled with normal finger force; thus requiring a wrench with an appropriate mechanical advantage. Also, it necessarily follows that the members can not be disassembled without a wrench. Thus, an apparatus and method for assembling and disassembling the threadably engageable members of such devices has to be available in the art.
The technique of assembling and disassembling acoustic members of surgical devices is dependent upon a number of constraints. For example, the structure and size of the threaded joint between the members is desirably as small as possible to minimize the weight and to minimize visual interference with the surgical procedure. Because of such size constraint, overtightening of the threaded joint is undesirable since overtightening may overstress the joint, resulting in its fracture. In contrast, insufficient tightening can result in incomplete acoustic coupling, heating of the threaded joint, reduced surgical performance and a potential for failure of the acoustic parts.
U.S. Pat. No. 4,832,021 describes and claims an apparatus and method which satisfactorily deals with the above constraints and provides means whereby acoustic members may be properly assembled and disassembled. In particular, the apparatus of U.S. Pat. No. 4,832,021 comprises a surgical handpiece, a fixture comprising a body member, said body member including a defining means for defining a handpiece-receiving opening extending transversely therethrough for receiving said surgical handpiece therein, said body member including a securing means for securing said surgical handpiece in position in said handpiece-receiving opening, and a torquing wrench means, including a first socket having a first socket bore therethrough and which is open at both ends, which is retained in scissor-like cooperating relationship with said fixture for torquing an acoustic member to a predetermined torque value into place on said surgical handpiece, after passing an end of the acoustic member through said first socket bore, and while said securing means secures said surgical handpiece against rotation in and relative to said body member.
As stated above, the apparatus of U.S. Pat. No. 4,832,021 enables an operator to satisfactorily assemble acoustic members while applying the correct torque, but the apparatus itself comprises a number of distinct components which have to be assembled on and around the acoustic members to secure said members before the coupling torque is applied. Moreover, the torque limiting means is included in the wrench.
It has now been found that appropriate assembly and disassembly of threadably engageable members can be achieved by an apparatus which comprises only two operating components, wherein the component which holds and secures one of the members also includes the torque limiting means and the other component is the wrenching means, which accordingly may be simplified as hereinafter described.